Thermplastic olefins (TPOs) are uncrosslinked blends of olefin polymers and polyolefin elastomers. They can be made by physically blending in an internal mixer, or by polymerizing in a reactor. These materials are not paintable or coatable, because the paints or coatings consist of polar materials like urethanes, acrylics, epoxies, or melamines that have very poor adhesion to nonpolar materials like polyolefins. Typically an adhesion promoter is used as the tie layer between the TPO substrate and the paint coating. This extra step adds to the cost of the product, and the coating is not very durable.
European Patent Application 662,496 discloses a paintable or printable polymer composition consisting of a polyolefin or polyolefin/rubber blend and 0.1 to 10% by weight of at least one polymeric additive that is the reaction product of (a) a polyolefin or polyester modified by an unsaturated acid, ester or anhydride, and (b) an amine-, hydroxy-, or alkoxy-terminated polyoxyethylene, polyoxypropylene, or a copolymer of the two, e.g., the reaction product of a maleic anhydride-modified polypropylene wax and a methoxy-capped poly(ethylene oxide) glycol.
European Patent Application 634,424 discloses a blend of polypropylene with the reaction product of maleated polypropylene and a polyether amine. The blend displays improved paintability, improved impact resistance, and excellent mold flowability compared to blends of polypropylene and the reaction product of polypropylene and maleated polypropylene. However, the compositions disclosed in EP 662,496 and EP 634,424 are both lacking in durability.
Thus, there is still a need for a TPO composition that can meet the more stringent requirements for paint adhesion and durability that are required in today's marketplace, particularly in the automotive industry.